Music enhancement



g- 6, 1966 H. HURVITZ MUSIC ENHANCEMENT 2 SheetsSheet l Filed March 4, 1964 FIGJ H 4 \5 MUSIC Musm H $OUI2CE 7 SOU CE A} do C \O S mzvsee [2 F163 0 |e )7 u 1 14 \5 Musu: J BAL. 35% A 8 DEMODIW souece M00 SELECTOR J NOISE Powaz 2932c a 20 FM. $16.

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BAND DEMOD SOURCE MOD. SELECTOR REVERE 6 'fiJ I I 1 0 I I0 3 g muspc B 'v 233% 23 If souzce MOD SELECTOR 4 3OKC 2o INVENTOR HYMAN Huavl'rz ATTORNEYS 6, 1966 H. HURVlTZ 3,267,198

MUSIC ENHANCEMENT Filed March &, 1964 2 Sheets-Sheet 2 sum l3 MUS\C BAL BAND DEMOD a SOUECE seuzcwoa Zn/92B MUSIC. EAL $5 1 SOURCE MOD SELECTOR Q5 (4 Demon.

ATTORNEYS 6 n; n j) (4 FIG-6 EEJ EII H l/ United States" Patent 3,267,198 MUSIC ENHANCEMENT Hyman Hurvitz, 822 Warner Bldg, Washington 4, D'.C.

Filed Mar. 4, 1964, Ser. No. 349,388 13 Claims. (Cl. 84-124) ing simultaneous application to all the results.

A crucial concept involved is that of heterodyning the output of an organ, or other musical source, to a supersonic side-'band,sthereafter passing the supersonic sideband through a static circuit which shifts phase as a function of frequency, and thereafter heterodyning the supersonic side-band back to its original value. The heterodyning oscillator (or oscillators) may be frequency modulated over a fairly wide band, at a vibrato rate, in response to noise, or slowly and sinusoidally. The effect of such modulation is to continuously vary the phase relations among the partials of the music. Additionally, the rate of change of phase provides a frequency shift, so that the output sound frequencies vary at vibrato rate and are not constant in frequency while variable in phase. The frequency deviation can be adjusted by adjusting the slope of the b/;f filter, or the deviationof the oscillator, or both, but, inherently, higher frequencies may be deviated more than lower, even within the same complex tone.

. In applying reverberators to organ outputs, these may be available in supersonic form, and may have been heterodyned to supersonic frequency for extraneous purposes, and in such case the required heterodyning facilities are already available for use in the present systems. However, in addition, the continuous change of frequency results in elimination of the audible effects of resonances due to the reverberator. This in turn implies that, where vibrato is not desired, or where the reverberator is to operate at audio frequency, as in the well known Hammond device, due to the frequency shifts and p shifts which take place in the output of the present system, even if the heterodyne oscillator is varied only slightly in frequency, .or at a rate far below the vibrato rate, resonances in the reverberator are masked to considerable extent. This occurs also in part because the /f circuit introduces delay in its own account, superposed on the delay of the reverberator, and this delay is a function of frequency, i.e. the network is dispersive. This implies that, in the present system, a single spring audio reverberator can be employed whereas Hammond (Meinema Patent #2,982,- 819) requires two or three springs of different effective lengths to mask resonances. 7

Further, as explained in Kahn, US, Patent #3,060,389, the use of a suitable /f network can symmetrize the output band, i.e. eliminate peaks of signals due to phase addition of frequencies. This is particularly important in phase locked organs, i.e. those utilizing divider chains as tone generators, where many such peaks can occur. It is also of importance in a spring reverberative system wherein the driver of the reverberator cannot readily respond to such peaks, if the driver is economically designed.

The supersonic wire reverberator, developed by Baldwin Co., has advantages over the audio wire reverberator, but these may be overshadowed by increased costs. The increased costs derive only from the heterodyning require- 3,267,198 Patented August 16, 1966 "ice ments, because supersonic reverberators require only one spring and are relatively free of noise and effects of external vibration, whereas audio reverberators require multiple springs and special provision for eliminating effects of external vibration. This difilculty is overcome, according to the present system, in that a need for the heterodyning circuits exists in any event, and apart from the supersonic reverberator. But, if an audio wire reverberator is employed, having only one spring, slow (1 c.p.s.) frequency phase and delay variations, in the output of the system, as a function of frequency, mask the effect of wire resonances because of the continuous variation of the signal information. The resonances in rever berators occur at sub-sonic frequency separations and hence are most serious for low frequencies, and despite introduction of chorus effect into the music. In supersonic reverberators the frequency swings of the heterodyne oscillators can extend over thousands of cycles, to mask the resonances. Audio frequencies cannot be deviated to this extent. One effective way of masking resonances is to combine the reverberator output with the original or direct output, and this effect is enhanced by the gb/f net- Work which reduces cancellation of the same frequencies deriving from the direct and reverberated channels.

Bode, who appears to have invented the 3/1 network, was concerned with obtaining a linear variation of phase with frequency. Random variation also has its place, particularly in the music art. Assume, for example, that the Bode filter is designed to have a slope as a function of frequency that has as many variations of slope as possible. In such case, and employing a heterodyne system in which an audio band is heterodyned up to a supersonic band passed through the filter, and then heterodyned down to audio, the heterodyned steps being accomplished by a frequency modulated oscillator, then the new audio band will have residual variations of frequency due to the filter, equal at each frequency to the slope of the /f filter for that frequency, at that time, recalling that the band is sweeping. Hence each partial would be subjected to random frequency modulation.

It is, accordingly, an object of the present invention to provide a system for randomizing phase relations among the tone frequencies of an electrical music system.

It is a further object of the invention to provide vibrato modulation in the output of a musical instrument.

It is still another object of the invention to provide a phase randomized vibrato modulation of electrical music tones.

It is still another object of the invention to provide a dispersive reverberator network.

Another object of the invention resides in the provision of novel reverberators having minimum resonance effects.

A further object of the invention is to provide means for removing peaks of energy from organ music, and particularly from reverberated organ music, by introducing a circuit at the input, or output, or both, of the reverberator which has a phase delay and time delay variable as a function of frequency.

A further object of the invention is to provide circuitry for permitting electrical combination of reverberated and unreverberated signals, Without appreciable phase cancellation. I

Still another object of the invention is to provide a system for randomizing phase, amplitude and frequency, of an audio signal, as a function of time.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a block diagram of a modification of the invention having a dispersive reverberator;

FIGURE 2 is a block diagram of a modification of the system of FIGURE 1;

FIGURE 3 is a block diagram of a supersonic phase randomized music system;

FIGURE 4 is a block diagram of a modification of the system of FIGURE 3 employing a supersonic reverber ator;

FIGURE 5 is a block diagram of a modification of the system of FIGURE 4;

FIGURES 6 and 7 are block diagrams of further modification of the system of FIGURE 5; and

FIGURES 8, 9 and 10 are block diagrams of variant audio systems employing wire reverberations and phasefrequency systems.

In the drawings, generally, 10 is a source of music, i.e. an electric organ, or a microphone, or a phonograph or tape recorder, or generally a transducer which producesa band of tone frequencies. 11 is a passive circuit of the Bode type (U.S. Patent #1,828,454) which provides a phase shift which is a preselected function of frequency, including linear and non-linear, of large slope but of flat amplitude characteristic, hereinafter called an /f filter. 12 is a wire reverberator of the audio type and 13 of the supersonic type. 14 are amplifiers and 15 speakers. 16

4 FIGURE 4 FIGURE 4 is essentially FIGURE 3 with awire reverberator 13 added directly-in series with 5/ network 11. The /f network provides a dispersive reverberative characteristic, when taken in conjunction with the reverberator, which at least approximately has a fixed /f characteristic. Unreverberated signal can be added electrically to the output by channel 22 if desired, where 1 upon the phase cancellations usually produced by such are balanced amplitude modulators, 17 single side band.

filters, 18 heterodyne demodulators, and 19 heterodyne oscillators, 20 frequency modulators for the oscillators 19.

FIGURE 1 Music source 10 supplies tone signal in cascade to /f filter 11, audio wire reverberator 12, amplifier 14 and speaker 15. A parallel path exists at will, via switch S, from source 10 to amplifier 14. With switch S open, zfi/f filter disperses the phases and time delays of the tone signal frequencies widely, while 12 produces a fairly uniform delay, but has resonances spaced apart sub-sonically. The signal applied to the delay line 12 is then symmetrical (U.S. Patent #3,060,389 to Kahn), and the overall eifect is that of a dispersive reverberator. This is particularly valuable if 10 is an organ having phase locked tone generators, since the phases become dispersed, i.e. each frequency has a different delay time and phase, and phase delay per octave can be a random number, i.e. 27, so that no two partials of a phase locked set of oscillators will ever coincide in phase.

If switch S is closed the reverberated and unreverberated signals add, but there is never complete phase cancellation for more than one partial of notes of any single nomenclature, because one path to amplifier 14 is dispersive and the other is not.

FIGURE 2 2 FIGURE 2 is generally like FIGURE 1, and has its advantages, but the fact that reverberator 12 is in parallel with /f filter 11 implies that the two inputs to amplifier 14 are attenuated more or less alike, whereas in FIG- URE 1 the direct channel via switch S has no attenuation and the other channel has double attenuation.

FIGURE 3 The audio signal supplied by music source 10 .is heterodyned to supersonic value in balanced modulator 16, which is supplied with a frequency modulated oscillator. The supersonic frequency band can be varied at vibrato rate over a wide deviation, i.e. sever-a1 kc. When this frequency modulated Wave is treated by /f filter 11 the result is a varying phase superposed on a fixed phase separation among all the frequencies of the supersonic hand. These are retained at the output of the modulator, so that the sound acoustically radiated by speaker 15 is provided with vibrato and also phase ran-- domized by the noise power of oscillator 19.

addition are eliminated by the different phase shift characteristics of 11 plus 13, as against 22, i.e. if cancellation occurs for one partial of a tone all other partials will fail to cancel.

FIGURE 5 The system of FIGURE 5 follows that of FIGURE 4 except in that supersonic feed-back occurs from the output of reverberator 13 to the input of /f network 11,

via amplifier 23. Amplifier 24 is used for isolation and amplifier 23 is low gain, i.e. less than 1 (cathode. follower). By virtue of this feed-back, phase separations caused by /f network are increased, yet possibility of complete cancellation of more than an occasional partial does not exist.

FIGURE 6 This figure is similar to FIGURE 4, exept that the unreverberated sound is added to the output directly as audio, via channel 27.

FIGURE 7 In this figure, compared with FIGURE 6, the supersonic reverberator 13 is removed and an audio reverberator 12 included in channel 27.

FIGURE 9 FIGURE 10 This system is FIGURE 8 with addition of unreverberated signal via amplifier 30, at will, to the audio output, and with audio feedback from the output of /f network 11 to the input of wire reverberator 12, via amplifier 31, at will. The feed-back amplifier 31 should have a gain of less than 1, to avoid danger of oscillation, but danger of phase cancellation of more than one partial of a complex tone is also removed by the 111/ network 11. The latter also smooths out power peaks caused by the reverberator and randomizes the output phases of the music source, if a phase locked source is employed.

Where wide frequency deviations are employed, yet the audio band being processed includes low frequencies, say to 16 c.p.s., use of a single frequency conversion is inadequate to separate out single side bands, while perand amplitude occur. These are communicated to the audio tones, in which also occurs noise randomization of phase, due to the presence of the 6/) network.

If the /f network has a /f characteristic providing a given phase shift per octave, rather than a linear characteristic, then phase shift is percentagewise, i.e. a 10% shift, for example can occur at c.p.srand at 5,000

c.p.s. That this is feasible is indicated by US. Patent #3,060,3 89 to Kahn, or by Lundry #2,859,414, particu larly FIGURE 14. The Kahn circuit is particularly adapted to eliminating power peaks in audio circuits, and is for that purpose. It provides an inverse delay with frequency, i.e. higher frequencies are delayed less than lower frequencies. But phase shift is greater as a direct function of frequency. These characteristics are by no means inconsistent, since 21r radians at 1000 c.p.s. obviously involves less time than 211- radians at 100 c.p.s. by a factor of 10. Where the input to the Kahn network is frequency modulated, these characteristics oppose one another in producing frequency modulated outputs. But, frequency modulation due to phase delay is a function of slope of the phase delay curve, whereas frequency shift due to time delay is not.

As stated in the Kahn patent the network can be disposed to provide increased time delay with increasing frequency, if desired.

It is also clear that any time delay between modulator and demodulator, for example in FIGURES 3 to 8 inclusive, which is not compensated, will result in a change of output frequency at the speaker. This change is random, if oscillator 19 is randomly modulated, as by the noise source power supply. Hence, the system of FIG- URE 3, for example, provides randomized phase, frequency and amplitude of output, and the phase and frequency variations can be arranged proportional to audio frequency by selecting network 11 to have a rising time delay and a rising phase delay slope as a function of frequency, and properly selecting the slope. This improvement obviously extends to each of FIGURES 3-8, if noise B+ is used for the local oscillator, and Without requiring a frequency modulator.

In FIGURE 8, the output of organ is applied to heterodyne modulator 16, which is also supplied with output from oscillator 19, say at 30* kc. The latter may be frequency modulated by modulator 20, say at t3 kc. deviation and at 6 c.p.s. rate.

One side band is selected by filter 17. As in FIGURES 3 to 7, the filter 17 cannot always select only one sideband, due to the frequency modulation, if used, but this does not detract from the operation. So, the filter may have a pass band of 2740 kc. Of course, if no F.M. is employed, a pass band of 30-40 kc. may be used The selected side band is phase dispersed by /f circuit 11, and thereafter the audio is reconstituted by demodulator 18. The audio may be radiated by speaker 15, if switch 40 alone is closed; or via reverberator 13, if switch 41 alone is closed. Or, switches 40 and 42 may be closed to provide pseudo stereo, via speakers and 15a. Or, switches 41 and 42 may be closed.

A supersonic reverberator 13 may be applied in a separate channel 50, having its own demodulator 18a, and speaker 15b. The input to reverberator 13 may be directly applied via switch 51, or following /f filter 11, via switch 52.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

1. A music system, comprising a source of a band of tone signal, means for heterodyning said band of tone signal to a supersonic band, means for imparting to said supersonic band a variation of frequency, said last means comprising a circuit having substantially uniform amplitude versus frequency characteristic and a large shift of phase versus frequency, whereby shifts of frequency and relative phase with frequency occur in said supersonic band corresponding with said variation of frequency, and means for heterodyning the frequency varied supersonic band to an audio band of tone signal, whereby phases of the band of tone signals are randomized, and amplitude peaks are eliminated in said band of tone signals.

2. The combination according to claim 1 wherein the rate of frequency variation is a vibrato rate.

3. In an organ system having a phase locked array of oscillators for generating tones of a single nomenclature, means for displacing the relative phases of the partials of said tones comprising a passive circuit having a transfer characteristic as a function of frequency for said tones which is flat for amplitude and sloping for phase...

'4. In a music system, a source of complex tone signal, a wire reverberator having an input and an output, means connecting said source to said input, a passive circuit having a transfer characteristic as a function of frequency which is flat for amplitude and sloping for phase, means connecting said passive circuit in cascade with said wire reverberator to displace the phases of said complex tone signals.

5. In a music system, a source of a band of tone frequencies, a filter having a uniform attenuation characteristic as a function of frequency and a phase shift increasing continuously as a function of frequency over said band of tone frequencies, means for passing said band of tone frequencies through said filter, and a loudspeaker coupled to the output of said filter.

6. In a music system, an electric organ, an audio wire reverberator connected in cascade with said electric or- .gan, a filter having a uniform attenuation characteristic as a function of frequency and a phase shift continuously increasing as a function of frequency connected in series with said audio wire reverberator, and a loudspeaker connected in series with said filter.

7. The combination according toclaim 6 wherein is provided a feed-back path around said filter and said reverberator.

8. In a system for frequency modulating a band of frequencies, a filter having a pass band including a monotonic slope of phase as a function of frequency and a flat amplitude versus frequency characteristic, means for sweeping said band of frequencies with respect to said pass band.

9. In a system of frequency modulation of a band of audio frequencies, means for heterodyning said band of audio frequencies to a supersonic band of frequencies, said means including a heterodyne oscillator, means for varying the relative phases of the frequency components of said supersonic band of frequencies as a function of time, and means for heterodyning the phase varied frequency components to an audio frequency band, said last means comprising said heterodyne oscillator.

10. I-n a music system, a dispersive wire reverberator means having an input and output, a source of music con nected to said input, a speaker connected to said output.

11. A music system according to claim 10 wherein is provided an unrevenberated audio channel connecting said source of music and said speaker in shunt to said dispersive wire reverberator means.

'12. In a music system, a filter having a flat frequency response with frequency and a monotonic phase shift as a function of frequency, a wire reverberator connected in parallel with said filter.

13. In a music system, a dispersive reverberator including a Wire reverberator and a filter in series with said wire reverberator, said filter having a fiat amplitude response with frequency and a monotonic variation of phase with frequency.

No references cited.

A-RTHU-R GAUSS, Primary Examiner.

D. D. FO'RREJR, Assistant Examiner. 

1. A MUSIC SYSTEM, COMPRISING A SOURCE OF A BAND OF TONE SIGNAL, MEANS FOR HETERODYNING SAID BAND OF TONE SIGNAL TO A SUPERSONIC BAND, MEANS FOR IMPARTING TO SAID SUPERSONIC BAND A VARIATION OF FREQUENCY, SAID LAST MEANS COMPRISING A CIRCUIT HAVING SUBSTANTIALLY UNIFORM AMPLITUDE VERSUS FREQUENCY CHARACTERISTICS AND A LARGE SHIFT OF PHASE VERSUS FREQUENCY, WHEREBY SHIGTS OF FREQUENCY AND RELATIVE PHASE WITH FREQUENCY OCCUR IN SAID SUPERSONIC BAND CORRESPONDING WITH SAID VARIATION OF FREQUENCY, AND MEANS FOR HETERODYNING THE FREQUENCY VARIED SUPERSONIC BAND TO AN AUDIO BAND OF TONE SIGNAL, WHEREBY PHASES OF THE BAND OF TONE SIGNALS AR E RANDOMIZED, AND AMPLITUDE PEAKS ARE ELIMINATED IN SAID BAND OF TONE SIGNALS. 